(1) Technical Field
The present invention relates to a method for measuring strain and, more particularly, to a method for measuring circumferential strain from radially-tagged, short-axis magnetic resonance imaging (MRI) of an object.
(2) Background
As the heart beats, the heart's wall contracts longitudinally and rotates laterally. During a heart contraction, the cardiac muscle along the short-axis (SA) of the heart thickens in response to the longitudinal and lateral contraction of the heart. Infracted myocardium reduces the effectiveness of the heart contraction and may be detected by calculating circumferential strain.
Circumferential strain is a quantitative value used to describe the regional and global amplitude of a myocardial contraction and is an important parameter in the quantitative evaluation of heart failure. Clinically, this quantitative evaluation may be used to describe the strength of a heart contraction.
Several methods currently exist for calculating the circumferential strain in the heart. Tagging the SA slices in the radial direction by appropriate modulation of the longitudinal magnetization produces information that can be used to calculate circumferential strain.
Although methods vary, in general, most calculations of this strain are accomplished by using a particle tracking method. Strain calculation therefore comprises particle tracking to obtain the displacement field of the beating heart, followed by spatial differentiation of the obtained displacement field, which is a very noise sensitive process. Therefore, calculation of strain usually requires a time consuming and inaccurate image processing.
One method of determining through plane strain is Strain ENCoding (SNEC) Magnetic Resonance Imaging (MRI). SNEC MRI calculates the through plane strain for an imaging plane. SNEC MRI is unable to encode the in-plane strains including circumferential strain.
Therefore, what is needed is a method for encoding the circumferential compression of the heart in a robust way, without taking spatial derivatives and with the ability to measure strain along several SA planes simultaneously and in real-time. There also exists a need for a method for measuring the regional circumferential strain in the SA planes with minimal calculations for tissue tracking. Finally, a need also exists for a method for calculating circumferential strain that may be combined with a different kind of different MRI pulse sequences.